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  <div class="section" id="module-gzip">
<span id="gzip-support-for-gzip-files"></span><h1>12.2. <a class="reference internal" href="#module-gzip" title="gzip: Interfaces for gzip compression and decompression using file objects."><tt class="xref py py-mod docutils literal"><span class="pre">gzip</span></tt></a> &#8212; Support for <strong class="program">gzip</strong> files<a class="headerlink" href="#module-gzip" title="Permalink to this headline">¶</a></h1>
<p><strong>Source code:</strong> <a class="reference external" href="http://hg.python.org/cpython/file/2.7/Lib/gzip.py">Lib/gzip.py</a></p>
<hr class="docutils" />
<p>This module provides a simple interface to compress and decompress files just
like the GNU programs <strong class="program">gzip</strong> and <strong class="program">gunzip</strong> would.</p>
<p>The data compression is provided by the <a class="reference internal" href="zlib.html#module-zlib" title="zlib: Low-level interface to compression and decompression routines compatible with gzip."><tt class="xref py py-mod docutils literal"><span class="pre">zlib</span></tt></a> module.</p>
<p>The <a class="reference internal" href="#module-gzip" title="gzip: Interfaces for gzip compression and decompression using file objects."><tt class="xref py py-mod docutils literal"><span class="pre">gzip</span></tt></a> module provides the <a class="reference internal" href="#gzip.GzipFile" title="gzip.GzipFile"><tt class="xref py py-class docutils literal"><span class="pre">GzipFile</span></tt></a> class which is modeled
after Python&#8217;s File Object. The <a class="reference internal" href="#gzip.GzipFile" title="gzip.GzipFile"><tt class="xref py py-class docutils literal"><span class="pre">GzipFile</span></tt></a> class reads and writes
<strong class="program">gzip</strong>-format files, automatically compressing or decompressing the
data so that it looks like an ordinary file object.</p>
<p>Note that additional file formats which can be decompressed by the
<strong class="program">gzip</strong> and <strong class="program">gunzip</strong> programs, such  as those produced by
<strong class="program">compress</strong> and <strong class="program">pack</strong>, are not supported by this module.</p>
<p>The module defines the following items:</p>
<dl class="class">
<dt id="gzip.GzipFile">
<em class="property">class </em><tt class="descclassname">gzip.</tt><tt class="descname">GzipFile</tt><big>(</big><span class="optional">[</span><em>filename</em><span class="optional">[</span>, <em>mode</em><span class="optional">[</span>, <em>compresslevel</em><span class="optional">[</span>, <em>fileobj</em><span class="optional">[</span>, <em>mtime</em><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><big>)</big><a class="headerlink" href="#gzip.GzipFile" title="Permalink to this definition">¶</a></dt>
<dd><p>Constructor for the <a class="reference internal" href="#gzip.GzipFile" title="gzip.GzipFile"><tt class="xref py py-class docutils literal"><span class="pre">GzipFile</span></tt></a> class, which simulates most of the methods
of a file object, with the exception of the <tt class="xref py py-meth docutils literal"><span class="pre">readinto()</span></tt> and
<tt class="xref py py-meth docutils literal"><span class="pre">truncate()</span></tt> methods.  At least one of <em>fileobj</em> and <em>filename</em> must be
given a non-trivial value.</p>
<p>The new class instance is based on <em>fileobj</em>, which can be a regular file, a
<a class="reference internal" href="stringio.html#StringIO.StringIO" title="StringIO.StringIO"><tt class="xref py py-class docutils literal"><span class="pre">StringIO</span></tt></a> object, or any other object which simulates a file.  It
defaults to <tt class="xref docutils literal"><span class="pre">None</span></tt>, in which case <em>filename</em> is opened to provide a file
object.</p>
<p>When <em>fileobj</em> is not <tt class="xref docutils literal"><span class="pre">None</span></tt>, the <em>filename</em> argument is only used to be
included in the <strong class="program">gzip</strong> file header, which may include the original
filename of the uncompressed file.  It defaults to the filename of <em>fileobj</em>, if
discernible; otherwise, it defaults to the empty string, and in this case the
original filename is not included in the header.</p>
<p>The <em>mode</em> argument can be any of <tt class="docutils literal"><span class="pre">'r'</span></tt>, <tt class="docutils literal"><span class="pre">'rb'</span></tt>, <tt class="docutils literal"><span class="pre">'a'</span></tt>, <tt class="docutils literal"><span class="pre">'ab'</span></tt>, <tt class="docutils literal"><span class="pre">'w'</span></tt>,
or <tt class="docutils literal"><span class="pre">'wb'</span></tt>, depending on whether the file will be read or written.  The default
is the mode of <em>fileobj</em> if discernible; otherwise, the default is <tt class="docutils literal"><span class="pre">'rb'</span></tt>. If
not given, the &#8216;b&#8217; flag will be added to the mode to ensure the file is opened
in binary mode for cross-platform portability.</p>
<p>The <em>compresslevel</em> argument is an integer from <tt class="docutils literal"><span class="pre">0</span></tt> to <tt class="docutils literal"><span class="pre">9</span></tt> controlling
the level of compression; <tt class="docutils literal"><span class="pre">1</span></tt> is fastest and produces the least
compression, and <tt class="docutils literal"><span class="pre">9</span></tt> is slowest and produces the most compression. <tt class="docutils literal"><span class="pre">0</span></tt>
is no compression. The default is <tt class="docutils literal"><span class="pre">9</span></tt>.</p>
<p>The <em>mtime</em> argument is an optional numeric timestamp to be written to
the stream when compressing.  All <strong class="program">gzip</strong> compressed streams are
required to contain a timestamp.  If omitted or <tt class="xref docutils literal"><span class="pre">None</span></tt>, the current
time is used.  This module ignores the timestamp when decompressing;
however, some programs, such as <strong class="program">gunzip</strong>, make use of it.
The format of the timestamp is the same as that of the return value of
<tt class="docutils literal"><span class="pre">time.time()</span></tt> and of the <tt class="docutils literal"><span class="pre">st_mtime</span></tt> attribute of the object returned
by <tt class="docutils literal"><span class="pre">os.stat()</span></tt>.</p>
<p>Calling a <a class="reference internal" href="#gzip.GzipFile" title="gzip.GzipFile"><tt class="xref py py-class docutils literal"><span class="pre">GzipFile</span></tt></a> object&#8217;s <tt class="xref py py-meth docutils literal"><span class="pre">close()</span></tt> method does not close
<em>fileobj</em>, since you might wish to append more material after the compressed
data.  This also allows you to pass a <a class="reference internal" href="stringio.html#StringIO.StringIO" title="StringIO.StringIO"><tt class="xref py py-class docutils literal"><span class="pre">StringIO</span></tt></a> object opened for
writing as <em>fileobj</em>, and retrieve the resulting memory buffer using the
<a class="reference internal" href="stringio.html#module-StringIO" title="StringIO: Read and write strings as if they were files."><tt class="xref py py-class docutils literal"><span class="pre">StringIO</span></tt></a> object&#8217;s <a class="reference internal" href="stringio.html#StringIO.StringIO.getvalue" title="StringIO.StringIO.getvalue"><tt class="xref py py-meth docutils literal"><span class="pre">getvalue()</span></tt></a> method.</p>
<p><a class="reference internal" href="#gzip.GzipFile" title="gzip.GzipFile"><tt class="xref py py-class docutils literal"><span class="pre">GzipFile</span></tt></a> supports iteration and the <a class="reference internal" href="../reference/compound_stmts.html#with"><tt class="xref std std-keyword docutils literal"><span class="pre">with</span></tt></a> statement.</p>
<p class="versionchanged">
<span class="versionmodified">Changed in version 2.7: </span>Support for the <a class="reference internal" href="../reference/compound_stmts.html#with"><tt class="xref std std-keyword docutils literal"><span class="pre">with</span></tt></a> statement was added.</p>
<p class="versionchanged">
<span class="versionmodified">Changed in version 2.7: </span>Support for zero-padded files was added.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.7: </span>The <em>mtime</em> argument.</p>
</dd></dl>

<dl class="function">
<dt id="gzip.open">
<tt class="descclassname">gzip.</tt><tt class="descname">open</tt><big>(</big><em>filename</em><span class="optional">[</span>, <em>mode</em><span class="optional">[</span>, <em>compresslevel</em><span class="optional">]</span><span class="optional">]</span><big>)</big><a class="headerlink" href="#gzip.open" title="Permalink to this definition">¶</a></dt>
<dd><p>This is a shorthand for <tt class="docutils literal"><span class="pre">GzipFile(filename,</span></tt> <tt class="docutils literal"><span class="pre">mode,</span></tt> <tt class="docutils literal"><span class="pre">compresslevel)</span></tt>.
The <em>filename</em> argument is required; <em>mode</em> defaults to <tt class="docutils literal"><span class="pre">'rb'</span></tt> and
<em>compresslevel</em> defaults to <tt class="docutils literal"><span class="pre">9</span></tt>.</p>
</dd></dl>

<div class="section" id="examples-of-usage">
<span id="gzip-usage-examples"></span><h2>12.2.1. Examples of usage<a class="headerlink" href="#examples-of-usage" title="Permalink to this headline">¶</a></h2>
<p>Example of how to read a compressed file:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">gzip</span>
<span class="n">f</span> <span class="o">=</span> <span class="n">gzip</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="s">&#39;file.txt.gz&#39;</span><span class="p">,</span> <span class="s">&#39;rb&#39;</span><span class="p">)</span>
<span class="n">file_content</span> <span class="o">=</span> <span class="n">f</span><span class="o">.</span><span class="n">read</span><span class="p">()</span>
<span class="n">f</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
</div>
<p>Example of how to create a compressed GZIP file:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">gzip</span>
<span class="n">content</span> <span class="o">=</span> <span class="s">&quot;Lots of content here&quot;</span>
<span class="n">f</span> <span class="o">=</span> <span class="n">gzip</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="s">&#39;file.txt.gz&#39;</span><span class="p">,</span> <span class="s">&#39;wb&#39;</span><span class="p">)</span>
<span class="n">f</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">content</span><span class="p">)</span>
<span class="n">f</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
</div>
<p>Example of how to GZIP compress an existing file:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">gzip</span>
<span class="n">f_in</span> <span class="o">=</span> <span class="nb">open</span><span class="p">(</span><span class="s">&#39;file.txt&#39;</span><span class="p">,</span> <span class="s">&#39;rb&#39;</span><span class="p">)</span>
<span class="n">f_out</span> <span class="o">=</span> <span class="n">gzip</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="s">&#39;file.txt.gz&#39;</span><span class="p">,</span> <span class="s">&#39;wb&#39;</span><span class="p">)</span>
<span class="n">f_out</span><span class="o">.</span><span class="n">writelines</span><span class="p">(</span><span class="n">f_in</span><span class="p">)</span>
<span class="n">f_out</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="n">f_in</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
</div>
<div class="admonition-see-also admonition seealso">
<p class="first admonition-title">See also</p>
<dl class="last docutils">
<dt>Module <a class="reference internal" href="zlib.html#module-zlib" title="zlib: Low-level interface to compression and decompression routines compatible with gzip."><tt class="xref py py-mod docutils literal"><span class="pre">zlib</span></tt></a></dt>
<dd>The basic data compression module needed to support the <strong class="program">gzip</strong> file
format.</dd>
</dl>
</div>
</div>
</div>


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<li><a class="reference internal" href="#">12.2. <tt class="docutils literal"><span class="pre">gzip</span></tt> &#8212; Support for <strong class="program">gzip</strong> files</a><ul>
<li><a class="reference internal" href="#examples-of-usage">12.2.1. Examples of usage</a></li>
</ul>
</li>
</ul>

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